Studies will be conducted to determine the biochemical basis for the nutritional function of selenium in preventing the fibrotic degeneration of the pancreas in the chick. This syndrome, called Nutritional Pancreatic Atrophy, is the only clearly delineated pathological condition which results from uncomplicated Se deficiency, and therefore presents a unique opportunity to study biochemical functions of Se which are not related to those of vitamin E. Specifically, studies will be conducted to: a) characterize the subcellular distribution of Se in the chick pancreas with particular attention to any Se-containing proteins present, b) determine whether pancreatic endocrine function is affected by Se-deficiency, c) determine the biochemical basis for impaired methionine metabolism in Se-deficiency, and d) develop comparative genetic models of chicken lines with differential susceptibility to Se deficiency.